Immunity is that
that mechanism by which your body is protected from
invasion of external bodies, through its own
physiological or artificial means. The immune system
is the collection of organs and tissues involved in
the adaptive defense of a body against foreign
biological material.

It may be broken down into the adaptive immune
system, composed of four lymphoid organs (thymus,
lymph nodes, and spleen and sub mucosal lymphoid
nodules) and the group motile cells that are
involved in the body's defense against foreign
bodies. The term may also be used to refer to the
totality of a body's defense systems, encompassing
both the adaptive immune system.